Henry Ford once stated, “Mark my word: A combination airplane and motorcar is coming. You may smile. But it will come . . . ” (Henry Ford, Chairman, Ford Motor Company-1940). In fact, shortly after the Wright brothers' first flight, people have been looking for ways to combine aircraft and automobiles into one vehicle. In 1918, Felix Longobardi was issued the first patent (U.S. Pat. No. 1,286,679) for a multi-use vehicle also known as a roadable aircraft. Throughout the following 88 years, there have been numerous patents issued for vehicle concepts that are capable of both flying and driving. While there has been no shortage of inventions in this field, there have been no concepts which have met with commercial success.
In fact, the closest any of the prior art appears to have come to commercial viability is the invention of Moulton B. Taylor, U.S. Pat. No. 2,767,939 (the '939 patent). Five prototypes of the “Aerocar” described in that patent were built, and most of them successfully drove and flew. The Aerocar design was certified by the Civil Aeronautics Administration (CAA), the precursor to today's Federal Aviation Administration (FAA). However, the Aerocar was limited in its practicality for most pilots, not only because of compromised performance, but also because of the requirement for the pilot to physically get out of the vehicle and fold the wings of the vehicle into a trailer that was towed behind the car portion of the vehicle. This additional labor was unattractive to the pilot/customer, both because of the added workload and because some pilots were not comfortable detaching and attaching the wings to the aircraft.
The reasons for the lack of commercial success for the numerous previous roadable aircraft patents are as varied as the patents themselves. Some failed because the design was infeasible or unsafe. Others failed because the design was too complicated or too expensive to manufacturer, while most did not satisfy the customer's need. Regardless of the specific reason, to this day no design appears to have been practical enough to become a commercial success.
This is not too surprising when one considers the difference between an aircraft and automobile that must be reconciled for such a combination vehicle to be practical. One difference is the aircraft's wings. For flight, an aircraft requires long, high-aspect ratio wings. The high aspect ratio allows for increased efficiency and performance. In order for the vehicle to drive on the road, the wings must be dealt with. Most roadable aircraft can be classified by how they deal with the wings and tail of the vehicle when in driving mode. These classes are: VTOL (vertical take-off and landing), modular, and integrated.
VTOL aircraft typically either have very short wings or no wings at all. The idea is that if one is tired of being stuck in traffic, one could push a button, take off straight up and fly over the traffic jam. However, VTOL aircraft are much more akin to helicopters than the ‘hovercraft’ envisioned as flying cars. As with helicopters, VTOL vehicles generate lift by either helicopter-like blades or ducted fans which force a large amount of air downwards. This downwash will generally kick up a lot of dirt and rocks. The debris would be thrown into the neighboring cars and pedestrians thus making the idea of taking off in the middle of traffic infeasible. As a result, VTOL aircraft are generally restricted to taking off from a helipad or remote area away from persons and property.
An example VTOL aircraft is described in U.S. Pat. No. 5,115,996 (the “Mollar Skycar™). This vehicle has four ducted fans located at each end of the vehicle that rotate to provide the necessary lift. Once airborne, the ducted fans rotate to provide the necessary forward thrust. VTOL aircraft, while being able to takeoff and land like a helicopter, also inherit all the complexity, cost and disadvantages of helicopters. Because of the complexity, number of parts, and stability issues, VTOL aircraft are inherently complex and expensive to develop, build and maintain.
Modular aircraft typically look like traditional aircraft when the vehicle is configured for flight. When configured for driving, the vehicle's wings (and usually the tail section) are removed from the aircraft. This creates two problems. First, the vehicle's operator must manually remove the wings for driving and reattach the wings for flight. Some vehicles allow for a single operator to perform the function, while others require multiple persons. Regardless of the design, many operators do not feel comfortable in their own skills to attach the wings safely to the aircraft. Also, when the wings and tail are removed, the question becomes one of what to do with them. If the wings are left at the airport, then the operator must return to that same airport in order to fly. This defeats the freedom of having a roadable aircraft. Some modular aircraft solve this problem by allowing the wings to be towed behind the vehicle. The '939 patent is an example of a modular aircraft where the wings and tail are towed behind the vehicle.
Integrated aircraft keep the wings attached to the vehicle at all times. Typically the wings are folded, either mechanically or manually, alongside or in the body of the vehicle. An integrated vehicle with mechanically operated wings allows for the operator of the vehicle to convert from aircraft mode to automobile mode at the ‘touch of a button’. This may add a considerable amount of practicality to the vehicle.
Besides the wings, another aspect of an aircraft that is not directly compatible with an automobile is the propeller. The propeller is the most sensitive part of the aircraft to nicks and dents. Because of this, pilots are trained to run their hand over the propeller before each flight to check for damage. When driving down the road, rocks and other debris are often kicked up by traffic. In modular designs, the propeller is typically part of the structure that is removed in order to convert the vehicle into an automobile. Therefore, modular designs typically do not have to worry about the propeller when the vehicle is configured for driving. For integrated designs, the propeller is either removed, such as in U.S. Pat. No. 2,430,869, left attached to front of the vehicle (such as in the “Fusion” vehicle by Steve Nichols), or left attached to the rear of the vehicle. Some vehicles, which leave the propeller attached to the rear of the fuselage, allow the propeller to hang below the vehicle where it is still susceptible to road debris (such as in U.S. Pat. No. 3,371,886). In order to be practical, the propeller should be protected from road debris at all times, without the need for the operator to manually remove the propeller.
An aspect of an automobile that is not directly compatible with an aircraft is the fact that the back of an automobile is typically a blunt surface. The reason for this includes the need for a rear bumper, indicator lights (such as turn signals) and identification devices (such as license plates). Aircraft, on the other hand, have sharp trailing edges to reduce the aerodynamic drag while in flight. Having a blunt surface, such as that on the back of an automobile, would produce a substantial amount of drag on the vehicle when in the air. This extra drag is at least inefficient and may be unacceptable. Modular designs with removable tail structures can hide the rear bumper and lights within the structure of the tail. However, integrated designs must deal with this problem. The prior art vehicles do not appear to address this issue. Either the vehicle has an automotive style aft end and takes the penalty in increased drag, or the vehicle has an aircraft aft end and does not address the need for bumpers or automotive lighting.
Finally, automobiles are typically designed to be strong and sturdy in order to survive the harsh environment of the road including potholes, bumps, curbs and other typical road hazards. This causes automobiles to be heavier than aircraft, which only have to deal with runways that are usually well paved. Fortunately, material technology is available now that allows for strong reliable structure at a fraction of the weight of previous automotive structures.
As such, while a number of roadable aircraft designs have been contemplated or produced, these designs have in general been impractical for use as general purpose driving and flying vehicles capable of meeting road and air vehicle safety standards.